Door heater



Oct. 15, 1968 Filed Nov. 16, 1966 M. K. ROHRS 3,405,922

DOOR HEAT ER I5 Sheets-Sheet 1 M. K. ROHRS Oct. 15, 1968 DOOR HEAT ER 6Sheets-Sheet 2 Filed NOV. 16. 1966 wmww M. K. ROHRS DOOR HEATER Oct. 15,1968 5 Sheets-Sheet 5 Filed NOV. 16. 1966 United States Patent O3,405,922 D0011 HEATER Bier-Vin K. Rohrs, Fanwood, Nl, assignor toAero-Flow Dynamics, Inc., (L. 3. Wing Mfg. Co. Division) Linden, NJ, acorporation of New York Filed Nov. 16, 1966, Ser. No. 594,379 14 Claims.(Cl. 26319) ABSTRACT OF THE DISCLOSURE Overhead door heater unit havingseparately subassembled burner section, horizontal duct section, blowersection, controls section, and downwardly projecting air dischargesection. Burner section includes line type, raw gas burner mounted atair inlet side of profile plate; airflow sensitive sail switch withinseparate opening of profile plate; and temperature high limit switch onprofile plate above burner. Duct section is unobstructed. Blower sectionincludes pair of laterally spaced apart blowers; temperaturedistribution 'baffie between blowers; air flow baflies at downstreamside of blower inlets; and Snorkels for cooling blower bearings.Discharge section includes vertical front plate particularly locatedwith respect to blower outlets; back plate at 52 angle; 122 expansionplates at sides; thermostat for controlling a temperature modulatingcontrol valve; and automatic reset high temperature limit switchadjacent blower outlets. Controls section includes said temperaturemodulating control valve in gas line section; solenoid actuated gasshut-off valve; and manual gas shut-off valve. Other features perspecification.

This invention generally relates to space heaters for heatingenvironmental air in factories, warehouses, commercial establishmentsand the like. Particularly, the invention relates to so-called doorheaters of the gas-fired type.

Door heaters are those which are mounted overhead adjacent to outsidedoorways or the like, especially doorways which are normally orfrequently opened, for the purpose of blowing heated air downwardly toshield the interior of the building from any inrush of cold air, and toheat any cold air which does enter through the open doorway. Suchheaters incorporate steam coils, gas flame, or sometimes electricalheating elements for heating the air which a contained blower drawstherethrough and discharges in the downward direction to form the airshield at the doorway. The incoming air to the heater may be drawneither from the outside of the building, as through an air ductconnecting the air-inlet side of the heater to the exterior atmosphere,or from within the building in the vicinity of the heater, the latterarrangement necessarily including the introduction of some fresh airsince the heater is adjacent an open doorway.

It is apparent that, to be effective, a door heater must emit a streamof uniformly heated air in a generally planar pattern of such height andwidth as to reach the floor and extend the width of the doorway, and insuch volume and direction, and with such force as to nullify andeffectively block the admission into the building of cold, outside airwhich will normally tend to enter through the doorway due to establisheddiiferences between interior and exterior temperature and pressureconditions, wind conditions and the like. Prior door heaters have notalways been adequate in these respects. Moreover, and of course,doorways are not all the same size, or even of standard sizes in heightand width, and the particular environmental conditions under which theheater must operate vary widely as between given locations of intendedinstallation. Prior heaters of a standard size and design are 3,405,922Patented Get. 15, 1968 more often suitable within only a limited rangeof application with respect to doorway size and operating conditionsand, therefore, manufacturing costs are usually abnormally high byreason of the need for frequent departures from the standard to adaptthe heater for a particular installation, or equivalent increased coststo the customer are involved by the need for installing two standardheaters where only one properly designed heater would do.

The present invention provides a door heater which is suitable for useunder a wide range of conditions of operation, such as higher or loweror narrower or wider doorway dimensions, anticipated large or smalltemperature variations, and other 'variable factors, without the needfor special adaptation of the unit to suit the given conditions. Thus,true rnass production techniques may be employed in its manufacture,thereby reducing the unit costs, and ultimate costs to the customer arereduced, especially in particular circumstances where the one unitadequately serves where normally two or more of the previously knowntypes of heaters would have been installed.

In the gas-fired door heater to be described, these result sare affordedby the overall arrangement of the heater, its inclusion of multiplespaced apart blowers and certain air baffling and air directioningelements, and other features, all of which provide improved air flowefiiciency through and out of the heater, very uniform temperaturedistribution throughout the emitted stream of heated air, and aparticular angular disposition of the emerging air stream. Thesecharacteristics measurably improve the suitability of the heater for useover a wide range of doorway sizes and other prevailing conditions.

In raw gas-fired door heaters, an additional problem is presented inthat insufficient air through the heater, as might be caused by blowerfailure, can cause incomplete combustion and resulting toxic fumes to beemitted. The heater of the present invention incorporates features whichautomatically prevent or discontinue emission of gas under suchcircumstances. One such feature is the inclusion of a sail switch forsensing the necessary flow of air. Although sail switches for thepurpose are known, the particular mounting and arrangement of it inaccordance with the invention provides more definite assurance of itseffective operation. Another such feature is the inclusion of anadditional so-called high-limit temperature switch which, in the heaterto be described, is actuated upon direct impingement of flame. Whilesuch switches have been used in gas-fired heaters of the type, theparticular location and setting of the switch is such that it will notbe actuated unless air flow through the heater is discontinued. Suchavoids spurious shutdown, while also assuring that shutdown will occurunder stated conditions.

Briefly and generally describing the invention in its preferredembodiment, within its elongated housing enclosure the heater includes aburner section, a duct and blower section, and a controls section, thesesections being in tandem alignment with each other. A fourth basicsection of the heater is its discharge section which is adjacent to theblower output, and projects below the underside of the main housing.

The burner section includes a single burner of the elongated, raw gastype, and a profile plate in surounding relation therewith to controland increase the velocity of the air flow through and around the burner.The aforementioned sail switch is mounted within a slot of the profileplate which provides a separate airstream for its actuation, and whichremoves it from the influence of excessively high temperatures. Thehigh-limit temperature switch is mounted on the air-inlet side of theprofile plate directly above the burner. The burner is electricallyignited by a conventional igniter, and includes a conventional flamesensing device, both of which are actuated in proper sequence bycontrols mounted in the controls section.

The duct and blower section includes a straight duct portion, extendingfrom the profile plate of the burner section, for unrestricted flow ofheated air to a pair of blowers. The blowers are aligned in spaced apartrelation in the transverse direction of the heater, and discharge theinitially horizontal air flow in downward direction. A temperaturedistribution bailie spans the spacing between the blowers, the bafiiefacing and altering the horizontal flow of air to the blowers from theburner. This temperature distribution bafile effects a more eventemperature distribution within the air stream at the outlet of thedischarge section, as will be later described in greater detail.Additionally vertically disposed baflles are situated and extend intransverse direction within the spacing between each of the respectiveblowers and the respectively adjacent side walls of the housing, and athird vertical bafile is similarly situated within the spacing betweenthe blowers, these baffles being in alignment with each other andlocated immediately rearward of the blower inlet openings, as will beseen. They extend the full height of the housing, and serve not only todeflect the flowing air into all four of the blower inlet openings, butalso serve to insulate the controls section from the influence of theheated air flow.

The control section mounts appropriate controller apparatus forinitiating, terminating and controlling the flow of raw gas to theburner, and for automatically modulating the gas fiow to effect constanttemperature of the heated air in accordance with any predeterminedtemperature setting. Temperature setting control is effected by acontrol knob which is exposed at the underside of the heater housing,the control knob being adapted to be engaged by a separate and speciallyformed cup-like adjustment device so that the adjustment may be remotelyeffected as is necessary by reason of the high elevation of the heaterwhen mounted overhead at a doorway.

The discharge section includes a vertical front plate and an angularlydisposed back plate which project below the underside of the mainhousing and between which the discharging heated air will flow. The backplate is disposed at an angle of 52 with respect to the horizontal,facing towards the air inlet end of the heater. At each of therespective ends of the discharge section (i.e., at the respective sidesof the heater unit), the discharge opening is terminated by an expansionplate which is disposed at an angle of 122 with respect to horizontal asmeasured from the plane of the discharge opening of the adjacent blower.In additon, within the path of the discharging air from each blowerthere are mounted two longitudinally extending vanes for pivotaladjustment in transverse direction.

These and other objects, features and advantages of the invention willbe more apparent from the following detailed description of a preferredembodiment thereof, when taken together with the accompanying drawingsin which:

FIGURE 1A is a diagrammatic, sectional side elevation showing, to areduced scale, of a typical gas-fired door heater installation at thedoorway of a loading platform or the like in a factory building;

FIGURE 1 is a top plan view of a gas-fired door heater in accordancewith the invention, its top panel being omitted for clarity;

FIGURE 2 is a sectional side elevation of the door heater, the viewbeing taken at lines 22 of FIGURE 1 and certain elements being omittedfor clarity;

FIGURE 3 is a somewhat enlarged end view of the airinlet end of the doorheater, the view being partially in cross-section as seen from line 3-3in FIGURE 1 and certain elements having been omitted for clarity; and

FIGURE 4 is a sectional end view, to the scale of FIGURE 3, of theopposite end of the door heater, the

4 view being taken at lines 4-4 in FIGURE 1 and partially broken away toshow certain details;

FIGURE 4A is an enlarged section side elevation showing a means foradjusting the temperature of the discharging air.

Referring first to FIGURE 1A, a gas-fircd door heater 10 in accordancewith the invention is mounted overhead at the interior side of anoutside doorway 11 of a factory building or the like, the floor of whichis indicated by reference numeral 12. The doorway 11 may have aconventional type overhead sliding door 13, which is shown in its up oropen position adjacent a ceiling 14. Where the doorway 11 is at a truckloading platform 15 or the like, the door 13 may remain open forrelatively long periods of time during which, especially in coldweather, large quantities of cool air tend to enter the building. Thedoor heater it) is intended to blow heated air H in downward and outwarddirection from its discharge opening 10a as shown, in the form of acurtain of warm air extending across the doorway opening, to eliminatedrafts and the reduction or disruption of established room temperaturesas would otherwise occur within the building by reason of the doorwaybeing open. A single unit 10 in its preferred embodiment has nominalmain body dimensions 55 /2" wide x 64" long x 19 /2" high, and has beensuccessfully tested on doorways as large as 17 high and 14' 4" wide.Even under extreme temperature, pressure and wind conditions, thepreferred embodiment will, on a conservative rating basis, efiicientlyservice a doorway up to 12 high and 10 wide. Further, by simplyincreasing the rating of its motor and blowers, it will service doorwaysas high as 22., or doorways adjacent to which there exists unusual windcondition, or unusually high negative pressure conditions within thebuilding. Of course, two or more door heater units 10 may be mountedsideby-side, spaced or not, to service very wide doorways as, forexample, those greater than 14' 16 wide.

FIGURE 1A shows that the gas-fired door heater 10 is suspended from apair of laterally extending angle iron supports 15, the integrallyformed hanger elements 17 or 17a (alternatively) of the unit 10 (FIGURES1, 3 and 4) being bolted thereto. Its air inlet end 10b is spacedhorizontally away from the doorway 11 as shown to facilitate entry ofoutside or make-up air C, and its top is preferably spaced verticallyaway from the ceiling 13 to facilitate the passage of recirculated air Rfrom the room interior to the inlet end 10b as shown. Alternatively, andalthough not illustrated, an inlet air duct may be installed connectingthe inlet end 10b directly to outside air, as though an opening formedin the outside wall 14a of the building. A gas service pipeline 18delivers raw gas fuel to the heater 10 and, although not illustrated, itwill be understood that an electric service line for the operation ofthe contained blower motors, solenoid switches, etc. also leads to theheater unit 10.

Referring now to FIGURES 1 and 2, the door heater 10 in the longitudinaldirection within its enclosed housing 19 includes four basic sections: aburner section which is generally indicated by reference numeral 20; aduct and blower section generally indicated by numeral 21; a controlssection indicated by numeral 22; and a discharge section 23 (FIGURE 2)at the underside of the housing 19. Air to be heated flows through theheater 10 in the direction of the arrows, the air entering through agrillwork (FIGURE 3) at its inlet end 10b and flowing first horizontallythrough the burner section 20 and the duct and blower section 21, andthen downwardly through the discharge section 23 to discharge at thedischarge opening 10a.

The draft through the heater is forced by a transversely spaced apartpair of centrifugal blowers, respectively identified by referencenumerals 24a and 24b, which discharge in the downward direction into thedischarge section 23 as shown. In the preferred embodiment, each bloweris rated at 1 HR, and both have a 1% diameter common shaft which isrotated at 1010 r.-p.m. by a 2 HF, 1750 r.p..m., S-phase, open dripprooftype motor 26 via a belt and pulley arrangement 27. Alternatively, forservicing larger doorways or doorways at which special conditionsprevail as previously mentioned, a 3 HP. motor may be used, and theblowers rotated at appropriately higher speed. The shaft 25 is journaledbetween a pair of bearings 28a, 28b these being mounted in conventionalmanner centrally of the outwardly facing air inlet openings 29a, 29b ofthe respective blowers 24a, 2417 as shown. Each blower 24a, 24b has asecond axial air inlet opening, respectively 30a, 30b, at its side whichfaces inwardly of the unit 10. Thus, the air flow through the duct andblower section 21 enters the two blowers via-a total of four blowerinlet openings, as will be understood. The driven pulley 31 of the beltand pulley arrangement 27 is attached to an outwardly projecting end 25aof the shaft 25 adjacent the blower 24b as seen in FIGURE 1, the drivepulley 32 being attached to the motor shaft 33. It should be here notedthat, in addition to being centrally spaced 10" from each other, eachblower 24a, 24b is spaced in transverse direction a distance of about 7"from that sidewall of the housing 19 which is adjacent to it. Moreover,the duct area of the duct and blower section 21, forward of the blowers24a, 241;, does not have baffling or other air directioning elementstherein. Apart from contributing to lower manufacturing costs, thisunrestricted duct area, and the transverse spacing apart of the blowersfrom themselves and from the housing sidewalls, as shown, smoothes theair flow and contributes to the air flow efficiency of the systern.

A pair of snorkel pipes 55a, 55b (FIGURES 1 and 2) are respectivelydisposed immediately above each of the blower bearings 28a, 28b, eachbeing attached to the side of its associated blower, as by strapconnections 56a, 56b, and each extending through the topwall of thehousing 19 as seen in FIGURE 2. Thus, the blowers 24a, 24b draw a small,continuously flowing quantity of outside air across their respectivebearings 28a, 28b for aircooling the same during operation.

The downwardly facing air outlet openings of the blowers 24a, 24b areadjacent to, and discharge air through the respective housing airopenings 1% of the same size and shape formed at the underside of thehousing 19, as will be better understood from FIGURES 2 and 4.

Referring to FIGURES 1 and 2, a temperature distribution bafiie 34,having height of 3 on either side of the elevational plane of the shaft25', spans across the 10" spacing between the 15" wide blowers 24a, 24bat the forward ends of their housing enclosures, i.e., the ends whichface towards the burner section 20. In the preferred embodiment, thetemperature distribution baffle 34 is creased transversely midway of itsheight as seen in FIGURE 2, to provide a vertical upper air deflectorportion 340, and rearwardly inclined lower air deflector portion 34b,which generally follow the curvature of the blower housings, as will beapparent. The temperature distribution baffie 34 provides evenness oftemperature distribution throughout the heated air as it dischargesthrough the discharge section 23. This will be more fully understoodafter considering the general arrangement of the heater 10, as will nowbe described.

Raw gas fuel enters the heater 10 from the exterior gas surface line 18,the line 18 being coupled by a coupling 18:: to a gas supply conduit 35which is mounted within the heater housing 19. The conduit 35 conductsthe gas to an elongated, line-type raw gas burner 43 within the burnersection 20. The conduit 35 and burner 43 are mounted by support brackets36-39. As it enters the conduit 35, the gas flows first through anormally closed, solenoid actuated shut-01f valve 40, thence Emergingfrom the manifold 43a via appropriate gas orifices t-herealong (notshown), the gas is mixed with combustion air derived from the incomingair to be heated, the combustion air entering the burner 43 via itscombustion air apertures 43b. The front face 430 of the burner iscompletely open, and is situated centrally of a 14 /2" x 28% profileplate opening, generally indicated by reference numeral 44 (FIGURE 3),which is provided by a transversely disposed profile plate adjacent, buta short distance behind the plane of the front face of the burner, asshown. The profile plate is actually formed by a framing including apair of transversely extending and centrally spaced apart plates 45, 46having respective flange portions 45a, 45!) which face inwardly in thedirection of air flow, the plates 45, 46 being attached at therespective opposite sides of the unit as by spot welding betweenrespective top and bottom transversely extending angle iron frame pieces47, 48 which also serve to constrict the opening 44 at its top andbottom. Burner 43 is 24" long X 6 /2" high at its front.

Thus, with respect to the function of the temperature distributionbafile 34 and referring first to FIGURE 2, air to be heated is drawninto the duct portion of the burner section 21 through the grillwork byaction of blowers 24a, 24b. As indicated by the arrows, the air flowsthrough the profile plate opening 4 around and through the burner 43, toemerge in stratums of heated air which in the vertical direction may bedescribed as: a hot stratum H extending towards the blowers from theburner 43 at the center of the opening 44, and relatively cooler airstratums H extending adjacent and respectively above and below thecentral hot stratum. Similar air temperature stratification occurs inthe transverse direction, as will be understood from FIGURE 1. That is,air flowing through the profile plate opening 44 at the respective sidesof the burner 43, rather than through the burner, is heated to a lesserextent and emerges into the duct section 21 in two respective airstratums H adjacent the hot centrally disposed air stratums H emanatingfrom the burner itself. Of course, the stratum H is actually continuous,in surrounding relation to the hotter stratum H The bafiie 34 tends toblock the otherwise direct flow of the hot central stratum H into theceutermost blower inlets 30a, 30b, and to divert the hot stratum to thetop, bottom and sides of the duct area where it mixes with the coolerstratums of air to promote uniform temperature throughout all of the airflowing into the blower inlet openings 29a, 29b, 30a and 30b. Thetemperature distribution bafl le 34 is sized and arranged to provideoptimum temperature distribution With in the total air flow at H as itemerges through the heater discharge opening 19a.

Referring to FIGURE 2, it will be noted that the height of the housingsof blowers 24a, 24b is such as to contact the top plate of housing 19 soas to avoid air-flow over and beyond the blower tops. Verticallydisposed and transversely aligned air flow bafiies 49, 50 and 51 (FIG-URE 1) respectively disposed at either side and attached between theblowers 24a, 24b immediately adjacent the rearward sides of their inletopenings 2%, 29b, 30a and 30b, as shown, assist air flow efficiency bymechanically turning the air into the blower inlet. The bafiles 49, 50and 51 extend the full height of the unit 10 (see FIG- URE 2) andthereby also separate the controls section 22 from the duct and blowersection 21, and protect the electrical and gas control apparatus withinthe former from the heat within the latter. As seen in FIGURES 1 and 2,the air flow bafiie 49 has a narrow vertical opening 52 for passage ofthe belt of the pulley system 27 therethrough.

As shown in FIGURE 2, the discharge section 23 includes a verticallydisposed front plate 23a and a fixed back plate 231:, the latter beingdisposed at an angle 0 equal to 52 with respect to the horizontal, sothat the downwardly emerging air from blowers 24a, 24b is deflected inangular direction generally towards the inlet end 10b of the unit, asindicated by the arrow. In addition, and referring to FIGURE 4, thedischarge section 23 includes fixed expansion plates 230 at therespective opposite sides thereof, each plate 230 being disposed at adownward and outwardly flaring angle equal to 122 with respect to thehorizontal, as shown. In addition to permitting diverting of theemerging high velocity air towards the respective sides of the unit, theexpansion plates 230 permit expansion of the heated air and contributeto the efliciency of its discharge from the blowers, the particularangular disposition of the plates having been found to be optimum forthe purpose. Diverting of the discharge air to the respective sides iscontrolled by the setting of the respective independently positionablevanes 23d, two of which are mounted in alignment with the discharge fromeach blower 24a, 24b as shown in FIGURE 4. Each adjustable vane 23d ismounted for pivotal movement in transverse direction as indicated by thearrows, about pivot points 23e, to any desired position. The expansionplates 23c and vanes 23d adapt the heater 10 to serve a wide range ofdoorway widths, up to about 14' 6". Further, it will be noted that, asshown in FIGURE 2, each vane 23d in the longitudinal direction haslength substantially equal to the length, about 8 /2", of the dischargeopening of its associated blowers 24a or 24b, whereas the vertical frontplane 23a of the discharge section is located about 1 /2" forward (ie.,towards inlet end 10b) of the forward, curved end of the blowerdischarge opening. At its upper extremity, where its front and backplates 23a, 23b are joined to the underside of the housing 19, the widthof the discharge section 23 (i.e., in the longitudinal direction as seenin FIGURE 2) is therefore approximately 10". The depth of the dischargesection, as measured below the underside of the housing 19, is 4 /2".Considering the width and depth of the discharge section 23, thepositioning relative to the blower outlet of its front plate 23a, andthe 52 angular disposition of its back plate 23b, the resutling angle ofair discharge in the forward direction has been found to :be mosteffective in causing the heater 10 to be suitable for use at any of avariety of doorway heights.

At 1010 rpm. each blower 24a, 24b delivers 2800 c.f.m. The same blowerscan be rotated faster, by changing the size of the pulleys of the pulleysystem 27, to deliver 3250 c.f.m. per blower, if desired.

The burner 43 has a turn down ratio of :1, its rating being from 150,000B.t.u./hr. to 750,000 B.t.u./l1r. Although not shown in detail, it isignited by a conventional spark ignition system whose transformer 60 ismounted on profile plate 46, as indicated in FIGURES 2 and 3. Anelectrical connection box 61 is mounted therebelow for making wiringconnections (not shown). Referring to FIGURE 1, and as only partiallyindicated in FIGURES 2 and 3, a small 7 0D.) gas line 62 delivers afixed, continuously flowing supply of gas to the burner manifold 43afrom a takeoff location on the main gas conduit 35 between the manualshutoff valve 51 and the temperature modulation control valve 42. Thus,when the manual valve 41 is open and the solenoid valve 40 has beenelectrically opened, an initial small supply of gas flows to the burner43 for ignition by the conventional spark ignition system. Subsequent toignition, the gas line 62 continues to furnish a small, unmodulated,fixed input of gas to the burner, as aforesaid. However, the gas line 62might also include conventional flow control means (not shown) so thatthe line 62 would then function simply as a pilot gas line, gas flowtherethrough being terminated after burner ignition.

Although not illustrated, there is also mounted within the flame shield43d of the burner a flame sensing rod which is a part of a conventionallectronic flame safeguard device, whose actuating apparatus 63 ismounted on the control panel 64 within the controls section 22 of theunit, as shown in FIGURE 4. The flame sensing apparatus 63 is for theconventional purpose of sensing and monitoring the appearance of flamewithin the burner 43.

Also mounted on the control panel 64 is a magnetic starter 65 foractuating the blower motor 26. The control panel 64 also mounted aterminal board 66 and a fuse block 67 for necessary wiring connections.4

Referring again to FIGURE 3, safeguard against blower failure isprovided by a sail switch 63 and a manual-reset high limit switch 69,only a portionof theelectric wiring 70 to the latter being illustrated.These safeguard switches 68, 69 are electrically connected in serieswith the solenoid actuated gas inlet valve 40 so that, in the event offailure of the blowers 24a, 241; the valve 40 will automatically close,thereby cutting off all flow of gas'to the heater unit 10. This preventsemitting of toxic fumes from the heater, as might occur upon blowerfailure due to an insufliciency of draft air as is necessary forcomplete combustion of the raw gas fuel. Specifically, during normaloperation when the valve 40 is in opened condition as is maintainedelectrically by power to its incorporated solenoid, and while theblowers 24a, 24b are normally rotating so that a constant draft of airis passing through the unit, the normally open sail switch 68 is held inclosed (i.e. circuit-completing) condition by the deflecting force ofdrafted air on its sail element 68a as the air passes through theopening 72 (FIGURE 3) within which the sail 63a is mounted. The normallyclosed temperatureactuated, manual reset high-limit switch 69 adjacentthe burner 43 is also in closed condition. Should the blower motor 26fail, or the blowers 24a, 24b otherwise cease to rotate (as by aloosened connection to their shaft 25, etc.), the force of air willdiminish through the sail switch opening 72, whereupon the sail 68a willno longer be deflected and the sail switch 68 will open so that theseries circuit will be opened. The valve 40 should then close bydeactivation of its solenoid.

If for any reason the valve 40 fails to shutso that the feed of raw gascontinues, the gas flames or heat emating from burner 43 will then tendto rise vertically in the absence of draft air, which normally forcesthe heat and flames in horizontal direction. The vertically rising heatwill heat-up and expand the bi-metallic high limit switch 69 thereabove,the switch being set to trigger at 300 'F. Triggering of the switch 69will also break the circuit necessary for continued operation of valve40, whereupon the valve 40 should close.

The location of the sail switch opening 72 within the profile plateelement 46, and therefore spaced away from the profile plate opening 44and burner 43, assures a steady, rather than turbulated flow of air pastthe sail element 68a responsive to the draft of blowers 24a, 24b whichdraws air directly through the opening 72. Elimination of turbulence orsimilar buifeting of the sail element 68a eliminates any tendency forintermittent on- .olf operation of the sail switch 68. In addition, thelocation away from the burner 43 retains the switch 68 in relativelycool condition to further assure its proper opera tion.

The location of the bi-metallic, high limit switch 69 above the burner43 and at the air-inlet side of the profile plate element 47 assuresthat it will remain relatively cool, and therefore will notactuate,"while th heater unit is operating normally. At the same time,it' is located such that it will promptly actuate upon impingement ofheat or flame rising from the burner 43 in the event of blower failure,as previously explained. Its setting is appropriate for the purpose. 7

The temperature of the heated air is regulated by adjustmentof therotatable knob 42a (FIGURES 2 and 4) of the modulating controlvalve 42.The knob 42a is exposed and accessible through a housing opening 19 11at the underside of the unit as shown, and its adjustment in eitherclockwise or counterclockwise direction adjusts the setting of the valve42 to provide a greater or lesser average flow of gas to the burner 43.The valve 42, itself, automatically further adjusts the gas flow inaccordance with its sensing of the actual temperature of the dischargingair to maintain a constant temperature air discharge. The valve 42 is ofa conventional self-contained, non-electrical, thermostatic type whichis actuated by the hydraulic pressure of a fluid which expands orcontracts in accordance with the temperature which a sensing instrument90 of the apparatus detects. The sensing instrument 90 is, of course,mounted within the air discharge section 23, as indicated in FIGURE 2.

An automatic reset type high limit switch 71 (FIGURE 2) is mountedwithin the discharge passage of at least one of the blowers 24a, 24b tomonitor air-discharge temperature therein for the purpose ofsafeguarding against failure in the operation of the modulating controlvalve 42. The switch 71 is electrically connected in series within theseries circuit which contains the blower-failure safeguard switches 68,69 and the solenoid actuated gas inlet valve 40. The switch 71 isnormally closed, thereby completing the electric circuit as is necessaryto continue the feed of gas. Should the modulating control valve 42 failto function and remain in its open condition in which a high rate of gasflows to the burner 43, the high limit switch 71, which is of anyconventional type for the purpose, will sense the abnormally hightemperature of the discharge air emanating from the blowers, and willautomatically open to cause a shutting of the main gas valve 40. Uponcooling, the switch 71 automatically closes.

FIGURE 4A illustrates the engagement of a special, cup-like adjustmentdevice 75 with the valve knob 42a for turning the latter, to avoid theuse of a step-ladder or the like as would otherwise be necessary tomanually turn the knob 42a, considering that the unit is mounted from 8to 17' overhead. The cylindrical cup-shaped adjustment device 75, whichis attached at the end of a pole 76 as by nails 76a, is open at itsouter end for receiving the knob 42a in surrounding relation as shown.It includes an oppositely disposed pair of detents 75a for engaging acorresponding pair of peripherally disposed grooves 42b formed in theknob 42a adjacent its underside, as shown. The device 75 is easilyinserted into and withdrawn from the housing aperture 19a whenadjustment is to be made. Of course, an appropriate temperature scale,or other knob setting indication, is marked on the housing 19 adjacentthe opening 19a, and on the knob 42a itself.

The general arrangement of the heater 10 is such that it may beconveniently manufactured in component subassemblies. That is, theburner 43 is part of a burner subassembly comprising the pair of angleiron frame elements 47, 48 having the oppositely disposed profile plateelements 45, 46 attached (as by welding) therebetween, the burner 43being mounted thereon by the attachment brackets 38, 39, as will beunderstood from FIGURE 3. The switches 68, 69, the transformer 60, andelectrical connections box 61 form a part of this subassembly. Referringto FIGURES 1 and 2, a blower subassembly is formed by the pair oftransversely exmending angle iron elements 57, 80, which are connectedby a longitudinally extending pair of triangular shaped and verticallydisposed side plates 81 at the respective sides of the unit, thusforming a frame on which both of the blowers 24a, 241) are mountedtogether with their baffle plates 34, 50, 51 and 52, and snorkel pipes55a, 55b. In addition, this blower mounting framework includes a thirdtransversely extending angle iron element 82 (FIGURES 2 and 4), to whichthe control panel 64 will be attached. The blower subassembly alsoincludes the motor 26 and its associated adjustable mounting apparatus83, and the belt and pulley arrangement 27. The gas pipe hanger straps36 and 37 also form a part of the blower subassembly. The dischargesection 23 is a separate subassembly comprising its front plate 23a, itsback plate 23b, expansion plates 23c, and respective outer side plates(unnumbered, but seen in FIGURE 4), the vanes 23d being pivotallymounted between the plates 23a, 23b as seen in FIGURE 2. Although notillustrated in detail, the horizontal duct or housing 19 is formed by apair of longitudinally extending, L-shaped duct portions attached inopposite, abutting relation along their horizontal lower leg portions,thus forming the bottom and side walls of the duct, and a pair ofremovable top panels which extend between the upwardly projecting sidewall portions. As seen in FIGURE 3, the side walls are bentlongitudinally, midway of their height, as are the respectively cofacingpair of triangular shaped vertical elements 81 of the blower subassembly(see FIGURE 2, for example). The two blower-air outlet openings 1% atthe underside of the housing 19 are respectively formed in the abuttingbottom wall portions of the 'housing, the connection between theL-shaped duct portions being midway of the width of the unit. Aspreviously mentioned, a framed grill-work is attached at the inlet end10b of the housing 19 and, as will be understood from FIGURE 2, aremovable panel 10d, is attached across the housing at its opposite end.The burner and blower subassemblies are attached to one of the L-sha-pedhalves of the housing 19, after which the other longitudinally extendingL-shaped half of the housing is attached, thus initially forming aU-shaped enclosure around these subassemblies. The piping 35, 62, valves40-42, and appropriate electrical wiring are mounted and connectedtherein, whereupon the top panel plates, hangers 17 or 17a, grill-workltlc, end closure panel 10d, and discharge section 23 are attached.

Thus has been described a gas-fired door heater which achieves all ofthe objects of the invention.

What is claimed is:

1. An air heater for mounting overhead at a doorway or the like,comprising horizontal duct means being open at a forward end thereof toprovide an air inlet, transversely disposed profile plate means withinsaid duct means near its said air inlet and defining a centrallydisposed profile plate opening smaller than the transverse area of saidduct means, air heater means adjacent said profile plate means forheating air passing through said profile plate opening, a pair ofcentrifugal blowers for inducing a flow of air from said duct means airinlet through said profile plate opening and having respective blowerhousings mounted within said duct means at a location spacedlongitudinally a distance away from said profile plate means and saidair heater means whereby said heating by said air heater means iscompleted before the air reaches said blower housings, said blowersbeing aligned with and spaced apart from each other in the transversedirection of :said duct means and each blower being spaced away from thesidewall of said duct means to which it is adjacent, each said blowerhousing having an axial air inlet opening at each side thereof and adownwardly facing air outlet opening, means defining an undersideopening of said duct means immediately adjacent and communicating witheach of said air outlet openings of the blower housings, respectively,and means defining an air discharge section projecting below said ductmeans, said air discharge section being in surrounding relation withrespect to both said underside openings thereof and having means formerging the air emanating from said air outlet openings of the blowerhousings into a single stream of substantially downward flowing airextending substantially the Width of said duct means between its saidsidewalls.

2. An air heater according 'to claim 1 which further comprises anair-temperature distribution bafiie spanning between said spaced apartblower housings at the end thereof which faces said profile plate means,said airtemperature distribution bafile having portions respectivelyextending above and below the horizontal axial plane of said blowers topartially block and deflect that portion of said flowing air as wouldotherwise flow directly to those of said blower inlet openings which aredisposed between said blowers.

3. An air heater according to claim 2 wherein the overall height of saidair-temperature distribution battle is substantially equal to one-third/3) the height of said horizontal duct means, said bafile portions beingsubstantially equal in height.

4. An air heater according to claim 2 which further comprises verticallydisposed air baffle means extending transversely of said duct meanswithin the respective spacings between said blowers and between eachsaid blower and the respectively adjacent sidewall of said duct means,said air baffle means being disposed substantially immediately adjacentsaid axial air inlet openings of said blowers at the side thereof whichis farthest from said forward end of the duct means.

5. An air heater according to claim 4 wherein each said blower housing,and said air baffle means, has height which is substantially equal tothe height of said duct means.

6. An air heater according to claim 5 wherein the interior of said ductmeans between said profile plate means and said air-temperaturedistribution baffie is substantially unobstructed with respect to saidflow of air from said profile plate opening to said air inlet openingsof the blowers.

7. An air heater according to claim 1 wherein said air discharge sectionprojecting below said duct means comprises a vertically projecting andtransversely extending front plate substantially adjacent that side ofeach said duct means underside opening which is nearest said forward endof the duct means, and a transversely extending back plate immediatelyadjacent that side of each said underside opening which is farthest fromsaid forward end of the duct means, said back plate being disposed at anangle substantially equal to fifty-two degrees (52) with respect to thehorizontal in direction towards said forward end of :the duct means.

8. An air heater according to claim 7 wherein the downwardly projectingheight of said discharge section is substantially equal to one-half /2)the width, as measured in the longitudinal direction of said duct means,of said underside openings of the duct means, said undersideopenings'having equal width, and said front plate of the dischargesection is spaced away from each said underside opening, in directiontowards said forward end of the duct means, a distance substantiallyequal to one third /a) of said height of the discharge section.

9. An air heater according to claim 8 wherein said discharge sectionfunther comprises a pair of air-expansion plates disposed between saidfront and back plates thereof, said expansion plates being respectivelydisposed substantially adjacent the respective outermost ends, in thetransverse direction of said duct means, of said underside openings ofthe duct means, each said expansion plate projecting downwardly from theunderside of said duct means at an angle substantially equal to onehundred twenty-two degrees (122) with respect to the horizontal indirection towards that sidewall of said duct means to which therespective expansion plate is adjacent.

10. An air heater according to claim 9 wherein said discharge sectionfurther includes a pair of longitudinally extending and transverselyspaced apart vanes mounted for adjustable pivotal movement within thedownwardly projected area of each of said underside openings of the ductmeans.

11. An air heater according to claim 1 wherein said 12. L a blowers havea common shaft of rotation, said shaft being journaled between a pair ofbearings, each bearing of the pair being mounted substantially withinone of said axial air inlet openings of one of said blower housings, andwhich further comprises a snorkel pipe communicating with the exteriorof said duct means and having an open end immediately adjacent each ofsaid bearings for aircooling the latter responsive to activation of saidblowers. 12. An air heater according to claim 1 wherein said air heatermeans comprises a line-type raw gas burner mounted centrally of saidprofile plate opening whereby a portion of said air flowing .throughsaid profile plate opening enters said burner to furnish comb ustion airtherein and the remaining portion flows around said burner, gas conduitmeans for feeding raw gas fuel to said burner, said gas conduit meanshaving an, electrically actuated gas shut-off valve therein, and meansresponsive to substantial absence of said flow of air for inducingautomatic closing of said shut-off valve, said flow responsive meanscomprising means defining a second opening through said profile platemeans at a location spaced away from the first said profile plateopening whereby a small additional flow of air passes through saidsecond opening from said duct means air inlet responsive to activationof said blowers, and a sail switch having a sail element mountedsubstantially within said second opening, said sail switch beingelectrically connected to said shutoff valve.

13. An air heater according to claim 12 wherein said flow responsivemeans further comprises a high-heat responsive switch mounted above saidburner on that side of said profile plate means which faces towards saidforward end of the duct means, said switch being electrically connectedto said sail switch and said shut-off vlave.

14. An air heater according to claim 1 wherein said air heater meanscomprises a line-type raw gas burner mounted centrally of said profileplate opening whereby a portion of said air flowing through said profileplate opening enters said burner to furnish combustion air therein andthe remaining portion flows around said burner, gas conduit means forfeeding raw gas fuel to said burner, said gas conduit means having anelectrically actuated gas shut-off valve therein, and means responsiveto substantial absence of said flow of air for inducing automaticclosing of said shut-off valve, said gas conduit means further having amodulating flow control valve therein at a location between saidshut-off valve and said burner, a thermostat adjacent at least one ofsaid blower outlet openings and connected to said fiow control valve formodulation of the latter responsive to the temperature at said locationof the thermostat, and a rotatable knob on said flow control valve foradjusting the temperature responsive range thereof, said knob beingexposed at the underside of said duct means.

References Cited UNITED STATES PATENTS Re 25,626 7/ 1964 Yeo et al.263-19 2,171,275 8/1939 Morrison 26319 2,604,313 7/1952 Grantham 263333,086,441 4/1963 London 9836 3,112,686 12/ 1963 Peterson 9836 3,210,05910/1965 Nesbitt et a1 263-19 FREDERICK L. MATTESON, 111., PrimaryExaminer.

E. G. FAVORS, Assistant Examiner.

